1. Field of the Invention
The present invention relates to semiconductor devices using oxide semiconductors and methods for manufacturing the semiconductor devices.
Note that one embodiment of the present invention is not limited to the above technical field. The technical field of one embodiment of the invention disclosed in this specification and the like relates to an object, a method, or a manufacturing method. In addition, one embodiment of the present invention relates to a process, a machine, manufacture, or a composition of matter. Specifically, examples of the technical field of one embodiment of the present invention disclosed in this specification include a semiconductor device, a display device, a liquid crystal display device, a light-emitting device, a lighting device, a power storage device, a storage device, a method for driving any of them, and a method for manufacturing any of them.
In this specification and the like, a semiconductor device generally means a device that can function by utilizing semiconductor characteristics. A display device, an electro-optical device, a semiconductor circuit, and an electronic device include a semiconductor device in some cases.
2. Description of the Related Art
In recent years, improvement in operation speed is required in semiconductor devices (e.g., a central processing unit (CPU) and a dynamic random access memory (DRAM)) including transistors. The resistance of a wiring connected to a transistor can be a factor that inhibits an improvement in operation speed; therefore, a reduction in wiring resistance is desired.
Conventionally, an aluminum film has been widely used as a material used for a wiring, a signal line, and the like. For further reducing the resistance, research and development of using a copper (Cu) film as a material is extensively conducted. However, a Cu film is disadvantageous in that adhesion thereof to a base film is low, dry etching thereof is difficult, and characteristics of a transistor easily deteriorates due to diffusion of Cu from the Cu film into a semiconductor layer of the transistor.
A silicon-based semiconductor material is widely known as a material for a semiconductor thin film applicable to a transistor, and as another material, an oxide semiconductor has been attracting attention (see Patent Document 1).
A transistor using an oxide semiconductor film is known to have an extremely low leakage current in an off state. For example, a low-power CPU and the like utilizing the low leakage current of a transistor using an oxide semiconductor film are disclosed (see Patent Document 2).
As a method for providing a transistor using an oxide semiconductor film with stable electrical characteristics, a technique for doping an oxide semiconductor film with oxygen is disclosed (see Patent Document 3). With the technique disclosed in Patent Document 3, the impurity concentration and oxygen vacancies in the oxide semiconductor film can be reduced. As a result, variation in electrical characteristics of the transistor using the oxide semiconductor film can be reduced and reliability can be improved.
Furthermore, a Cu—Mn alloy is disclosed as an ohmic electrode formed over a semiconductor layer including an oxide semiconductor material including indium (see Patent Document 4).
However, in the case where a transistor using an oxide semiconductor is used, part of the oxide semiconductor serves as a channel region, and there is a problem in that the transistor characteristics obtained in a gate BT stress test, which is one kind of reliability test of a transistor, deteriorate when Cu is diffused into the channel region.